linux-kernel - Re: [PATCH v5] RO/NX protection for loadable kernel modules

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Message-ID: <20090712173329.GB12054@kroah.com>
Date:	Sun, 12 Jul 2009 10:33:29 -0700
From:	Greg KH <greg@...ah.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>, Ingo Molnar <mingo@...e.hu>,
	Siarhei Liakh <sliakh.lkml@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	James Morris <jmorris@...ei.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@....de>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-cris-kernel@...s.com
Subject: Re: [PATCH v5] RO/NX protection for loadable kernel modules

On Sun, Jul 12, 2009 at 08:32:27AM -0700, Arjan van de Ven wrote:
> On Sun, 12 Jul 2009 19:28:27 +0930
> Rusty Russell <rusty@...tcorp.com.au> wrote:
> 
> > On Sun, 12 Jul 2009 05:15:24 pm Arjan van de Ven wrote:
> > > Rusty Russell <rusty@...tcorp.com.au> wrote:
> > > > (I like the idea of trying kmalloc and falling back, simply
> > > > because it reduces TLB pressure, but that's probably best done
> > > > after unification).
> > >
> > > or using a non-power-of-two get_free_pages() thing...
> > >
> > > some architectures will need to know that memory needs to be
> > > executable at allocation time so that it can be put in an
> > > executable address range etc...
> > 
> > Yes, maybe that's better than kmalloc.  On my laptop I have 105
> > modules loaded, with 3778464 total length: I'm wasting 206944 bytes
> > on unused tails of pages.  But that's only 0.06% of my memory.
> >
> 
> 105 is also a sign that you picked a somewhat suboptimal config...
> that's of course your choice but it's a choice that has a small price,
> if you don't want to pay that price, changing the config to not be
> entirely insane is a good answer as well ;-)

But this is the "common" case in the world of Linux where the distros
are forced to build everything as modules.  So it should be considered
as a very valid case, and not merely dismissed out of hand.

thanks,

greg k-h
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